FIG. 1 illustrates a prior art system where a voltage regulator 10 supplies a regulated voltage (Vout) at a certain current (ILOAD) to a remote load 12 (RLOAD) via two wires 14 and 15. The regulator 10 detects its output voltage near an output terminal of the regulator 10 and uses the sensed voltage as a feedback signal to maintain the output voltage at a specified level.
In applications where the lines (e.g., wires or other conductors) between the regulator 10 and load 12 are long, each line has a significant resistance (RLINE), which causes a voltage drop. Therefore, the voltage at the load is lowered by the voltage drop along the two lines. In the example of FIG. 1, although the regulator 10 is outputting a regulated voltage of Vout, the voltage across the load RLOAD is Vout−(ILOAD*2RLINE). If the wires 14/15 were 20 gauge, the resistance would be about 0.01 ohms/foot. If the load current ILOAD was 10 amps, and the two wires were each 10 feet, the voltage across the load 12 would be 2 volts less than the regulated output voltage.
To compensate for such voltage drops, it is known to provide remote sensing of the load voltage by connecting voltage sense lines to the load that conduct only a small current and thus have a low voltage drop. The remotely sensed voltage is then used as the feedback voltage for the regulator to maintain the voltage at the load at a specified voltage. Providing such long voltage sense cables adds expense and complexity to the circuit. Other drawbacks exist.
There are also regulator compensation circuits that are configured to output a specified voltage at the remote load, where the line resistance is known and compensated for in the regulator output voltage. The regulator then continually compensates for an increased or decreased voltage drop as the regulator supplies more or less current to the load during its normal operation. However, such circuits require prior knowledge of the lines' resistance and do not detect the actual voltage drop in the lines. Accordingly, such circuits also do not compensate for changes due to temperature or connector instabilities. Therefore, such circuits have limited utility and do not provide an accurate regulated voltage to the load.
What is needed is an improved technique for remote sensing of the voltage at a remote load that automatically compensates for actual voltage drops along lines of any length and resistance. The inventive technique described herein is referred to as virtual remote sensing.